The std::equal_to allows the equality comparison to be used as a function, which means that it can be passed as an argument to templates and functions. This is not possible with the equality operator == since operators cannot be passed as parameters.
Header File:
#include <functional.h>
Template Class:
template struct equal_to : binary_function { // Declaration of the equal operation bool operator() (const T& x, const T& y) const { return x==y; } // Type of first parameter typedef T first_argument_type; // Type of second parameter typedef T second_argument_type; // The result is returned // as bool type typedef bool result_type; }
Syntax:
std::equal_to <int> ()
Parameter: This function accepts the type of the arguments T, as the parameter, to be compared by the functional call.
Return Type: It return a boolean value depending upon condition(let a & b are 2 element):
- True: If a is equals to b.
- False: If a is not equals to b.
Below is the illustration of std::equal_to in C++:
Program 1:
// C++ code to illustrate std::equal_to #include <algorithm> #include <functional> #include <iostream> #include <vector> using namespace std;
// Driver Code int main()
{ // Initialise vectors
vector< int > v1 = { 50, 55, 60,
65, 70 };
vector< int > v2 = { 50, 55, 85,
65, 70 };
// Declaring pointer of pairs
pair<vector< int >::iterator,
vector< int >::iterator>
pairs1;
// Use mismatch() function to
// search first mismatch between
// v1 and v2
pairs1 = mismatch(v1.begin(), v1.end(),
v2.begin(),
equal_to< int >());
// Print the mismatch pair
cout << "The 1st mismatch element"
<< " of 1st container : " ;
cout << *pairs1.first << endl;
cout << "The 1st mismatch element"
<< " of 2nd container : " ;
cout << *pairs1.second << endl;
return 0;
} |
The 1st mismatch element of 1st container : 60 The 1st mismatch element of 2nd container : 85
Program 2:
// C++ program to illustrate std::equals_to #include <algorithm> #include <functional> #include <iostream> using namespace std;
// Template template < typename A, typename B,
typename U = std::equal_to< int > >
// Function to check if a = b or not bool f(A a, B b, U u = U())
{ return u(a, b);
} // Driver Code int main()
{ int X = 1, Y = 2;
// If X is equals to Y or not
cout << std::boolalpha;
cout << f(X, Y) << '\n' ;
X = -1, Y = -1;
// If X is equals to Y or not
cout << f(X, Y) << '\n' ;
return 0;
} |
false true
Reference: http://www.cplusplus.com/reference/functional/equal_to/